Thomas Thomson was born in Paterson, New Jersey. He was the youngest of 13 children, and was self-supporting from a young age. He worked at a silk mill as a weaver, and went to night school to learn shorthand and bookkeeping skills. He came to California in 1904 to attend UC Berkeley. Thomson graduated 5 years later and then completed his law degree in 1910, and was admitted to the bar in 1911.
He came to Fresno later that year to practice with Sutherland and Barbour (who later became a congressman). He later worked with Harris and Harris, then for a number of years as a sole practitioner. Thomson was also a Federal Bankruptcy Referee. In 1929, he was appointed Superior Court Judge by Governor C. C. Young, and later won successive terms in 1930, 1936, 1942, and 1948.
He was a member and Master in 1918 of Las Palmas Masonic Lodge No. 366, O.E.S. No. 295, the Fresno Sciots, the Shrine, past president of the Moose Lodge, member of Fresno Elks, Fraternal Order of the Eagle, Woodmen of the World, Modern Woodmen of America, and Fresno County Peace Officers Association.
Thomson was very active in the Fresno community. He was President of the Fresno County Bar Association, and sponsored a movement to create the 4th District Court of Appeal to sit in Fresno.
He was chairman of the Fresno County Red Cross, Executive Committee Member of the Fresno County Tuberculosis Society, a Director of the Kiwanis Club, and served 20 years on the Boy Scouts Sequoia Council Committee for Advancement. In 1948, he received the Silver Beaver, the Boy Scouts of America's highest award, signed by President Truman.